APPLICANT'S ABSTRACT: DynorphinA(1-17) is an endogenous opioid peptide, but considerable evidence indicates that it also acts through a non- opioid system. For example, it inhibits acetic acid-induced writhing, an effect not antagonized by naloxone, and inhibits the expression of morphine tolerance and dependence in morphine tolerant animals. Moreover, both these effects are also mediated by the des-Tyr peptide, dynorphinA(2-17), which has no opioid activity and does not bind to opioid receptors. Recently, we have obtained evidence that dynorphinA(2-17) binds to its own distinct, non-opioid receptors. The present proposal is designed to test the hypothesis that the non-opioid effects of dynorphin, in particular, its modulation of opioid tolerance/dependence, are mediated through these receptors. To test this hypothesis, we will 1) characterize in detail the pharmacological and biochemical properties of dynorphinA(2-17) binding sites which we have recently identified in brain, spinal cord and dorsal root ganglia; 2) purify and cDNA clone the receptor for dynorphinA(2-17); 3) determine the effect of altering endogenous levels of dynorphin, using anti-dynorphin antibodies, on tolerance development in strains of mice differing in the degree of tolerance they develop; and 4) search for polymorphic differences in opioid receptors that might account for differences in the ability of dynorphin to modulate the actions of these opioid receptors. Overall, this proposal is designed to test a novel hypothesis of the existence of a yet unknown dynA(2-17) receptor system which may play a role in opioid tolerance.